The existence of a phenomenon in phosphorus (P) nutrition comparable to the “Neish effect” in nitrogen (N) nutrition (an inverse relation between seawater N enrichment and carrageenan content) was investigated in the temperate red alga Chondrus crispus Stackhouse. Plants were preconditioned for 17 d and then cultured under varying enrichments of P (0, 3, 6, 10, 15 μM P·wk−1) and a constant N enrichment (53.5 μM N·wk−1) for 5 wk. Tissue total P, tissue total N, and carrageenan contents were then determined. Identical experiments were performed using C. crispus collected during the fall, winter, spring, and summer seasons. The procedure was repeated using material collected during the following fall season and cultured under constant P (6 μM P·wk−1) and varying N enrichments (0, 3, 6, 10, 25 μM N·wk−1). In the fall (P) experiment, carrageenan content was the highest [53.1 ± 0.3% DW (dry weight)], and tissue total P content was the lowest (1.71 ± 0.27 mg P·g DW−1) in plants that received no P enrichment. Carrageenan content was stable (46.1 ± 1.8% DW) for plants given enrichments of 3 μM P·wk−1 and greater. Thus, a decrease in carrageenan content, concomitant with an increase in tissue total P content, was observed, but only at tissue total P levels below 2 mg P·g DW−1. As these levels were always higher than 2 mg P·g DW−1 in the winter, spring, and summer experiments, carrageenan content remained constant within each season at 46.2 ± 1.3, 43.1 m 0.7, and 44.5 ± 0.6% DW, respectively. Nitrogen enrichment of plants collected in the fall did not affect carrageenan content, which was stable at 49.3 ± 0.9% DW. When these plants were compared with those of the previous fall experiment (6 μM P·wk−1 and 53.5 μM N·wk−1), a slight increase in carrageenan content was noted. Thus, at sufficiently high concentration, N also decreased carrageenan content in C. crispus. Phosphorus nutrition had no significant effect on photosynthesis versus irradiance parameters (Pmax, α, Rd, Ic, and Ik), the contents of the photosynthetic pigments chlorophyll‐a, phycoerythrin (PE), phycocyanin (PC), and allophycocyanin (APC), and the ratios PE:APC and PC:APC. In contrast, N nutrition affected both Pmaxand the photosynthetic pigment contents. The data indicate that N limitation reduces the number of phycobilisomes but not their size. The greater reduction in phycobiliprotein than chlorophyll‐acontent corroborates the natural bleaching phenomenon regularly observed in C. crispus populations during summer when N levels are generally low in seawater. These results suggest that C. crispus in the temperate waters of the Bay of Fundy may experience N limitation, but P limitation is unlikely.
MacLeod, J. A., Kuo, S., Gallant, T. L. and Grimmett, M. 2006. Seafood processing wastes as nutrient sources for crop production. Can. J. Soil Sci. 86: 631-640. Large quantities of wastes are generated in the processing of seafood such as shellfish, crustaceans and finfish. These materials contain appreciable amounts of plant nutrients which may be useful in cropping programs. Under some conditions the waste materials can be directly applied to soil but in other situations stabilization may be necessary. The method of stabilization will influence the availability of nutrients in various cropping programs. Composting with wood can effectively stabilize the waste but the slow mineralization of organic N can limit the usefulness of the compost. Combining the waste with calcium oxide (CaO) or hydrated lime [Ca(OH) 2 ] can produce a stable material with good nutrient availability. If application rates of various wastes are based on their nutrient content, the nutrient requirement of specific crops, and the heavy metal concentrations, then potential environmental problems associated with excess nutrient and heavy metal loadings can be minimized. Application of these materials to land can effectively supply nutrients to crops and minimize environmental damage due to inappropriate methods of disposal.Key words: Seafood waste, composting, lime stabilization, crop nutrients MacLeod, J. A., Kuo, S., Gallant, T. L. et Grimmett, M. 2006. Les déchets de la transformation des produits de la mer, source d'éléments nutritifs pour les cultures. Can. J. Soil Sci. 86: 631-640. La transformation des produits de la mer comme les mollusques, les crustacés et les poissons engendre beaucoup de déchets. Ces derniers renferment une quantité appréciable d'éléments nutritifs pour les plantes et pourraient avoir leur utilité en agriculture. Les déchets peuvent être épandus directement sur le sol dans certaines conditions, mais dans d'autres situations, une stabilisation s'impose. La méthode de stabilisation influera sur les éléments nutritifs disponibles pour diverses cultures. Ainsi, le compostage avec du bois stabilise les déchets, mais la lenteur avec laquelle l'azote se minéralise réduit parfois l'utilité d'un tel compost. En mêlant de l'oxyde de calcium (CaO) ou de la chaux éteinte [Ca(OH) 2 ] aux déchets, on obtient un matériau stable, riche en éléments nutritifs assimilables. On réduira au minimum les risques potentiels pour l'environnement associés à la surcharge d'éléments nutritifs ou de métaux lourds en fondant le taux d'application des déchets sur leur teneur en éléments nutritifs, les besoins de la culture et la concentration de métaux lourds. L'application d'un tel matériau sur les terres fournira efficacement les éléments nutritifs dont la culture a besoin et atténuera les dommages environnementaux attribuables aux méthodes d'élimination inappropriées.Mots clés: Déchets des produits de la mer, compostage, stabilisation par la chaux, éléments nutritifs pour les plantes Traditional nutrient cycling models tend to consider nutrie...
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